This invention relates to a coding method of coding a digital video signal by subjecting the digital video signal to redundancy reduction coding. This invention relates also to a coding device for use in carrying out the method.
Each of the successive pictures is called a frame when the digital video signal is, for example, a television signal. Redundancy reduction coding is effective to code the digital video signal into a coded video signal having a low bit rate. As the redundancy reduction coding, basic interframe predictive coding is known in the art. The basic interframe predictive coding makes use of a correlation factor between adjacent ones of the pictures or frames. In the basic interframe predictive coding, the redundancy reduction coding is carried out on a difference between corresponding picture elements of two successive pictures to provide a result of the basic interframe predictive coding.
Motion-compensated interframe predictive coding is also known in the art as the redundancy reduction coding. In the motion-compensated interframe predictive coding, a motion vector is detected which represents a movement of each picture element between two of pictures. The motion-compensated interframe predictive coding carries out interframe predictive coding of the digital video signal by using the motion vector.
Inasmuch as the motion-compensated interframe predictive coding is also carried out by using a correlation factor between two adjacent pictures like the basic interframe predictive coding, not only the basic interframe predictive coding but also the motion-compensated interframe predictive coding will be referred to as interframe coding.
Intraframe or inframe coding is still also known in the art as the redundancy reduction coding. The intraframe coding is carried out by using a correlation factor between the picture elements within each of the pictures. The intraframe coding is, for example, PCM (pulse code modulation) coding, intraframe predictive coding, orthogonal transformation coding, or vector quantization coding.
Such redundancy reduction coding is generally used in transmitting the digital video signal. However, the redundancy reduction coding is also used in a video signal processing system which is for use in a recording medium, such as a compact disk read-only memory (CD-ROM), to record and/or reproduce the digital video signal.
In the meanwhile, it may be preferable that the compact disk read-only memory can be operable like a video tape in performing not only a normal reproduction but also various other functions, such as a reverse reproduction, a high speed reproduction, scene skipping, an arbitrary reproduction of an arbitrary scene. However, it is difficult to perform the reverse reproduction when the digital video signal is subjected to the interframe coding alone. More specifically, the digital video signal is divided into a zeroth or leading frame to an end or trailing frame as leading through trailing compressed video signals subjected to the interframe coding. The digital video signal is successively recorded on the recording medium from the leading compressed video signal to the trailing compressed video signal in a normal order. Merely for convenience of description, the zeroth through the end frames may be understood to correspond to zeroth through end scenes, respectively. On carrying out the reverse reproduction, the digital video signal is reproduced from the recording medium in a reverse order from the end scene in response to a request issued by an operator or user to indicate the reverse reproduction.
In order to perform the reverse reproduction, an improved method is disclosed in a prior U.S. patent application Ser. No. 189,249 which was filed May 2, 1988, by Toshio Koga, Junichi Ohki, Mutsumi Ohta, and Hideto Kunihiro for assignment to the present assignee and c/o NEC Home Electronics, Ltd. The above-named Mutsumi Ohta is the instant applicant. The Ohta et al patent application corresponds to a prior Canadian patent application No. 565,485 which was filed Apr. 29, 1988. In the prior patent applications, the video signal processing system is called an image processing system. The digital video signal is called a sequence of image signals. In the improved method, the digital video signal is coded with the leading and the trailing frames subjected to the intraframe predictive coding and with the remaining frames subjected to the interframe predictive coding. According to the improved method, it is possible to carry out not only the normal reproduction but also the reverse reproduction. The improved method is, however, defective in that the reverse reproduction can not be performed when an interframe/intraframe adaptive coding is used as the redundancy reduction coding. In the interframe/intraframe adaptive predictive coding, the digital video signal is decoded into a decoded signal with a first result of the interframe coding and a second result of the intraframe coding alternatingly appearing in the coded signal. More specifically, the interframe coding and the intraframe coding are adaptively alternatingly carried out in consideration of an amount of produced information of the first result and another amount of produced information of the second result.